"The ingenious Douglas XB-42A Mixmaster was America's first 644 kph (400 mph) bomber. One of the most advanced reciprocating-engine aircraft flown, Douglas never produced it because it appeared late in the war as jet-propelled designs rendered nearly every propeller-driven aircraft obsolete. The Mixmaster's engines generated about the same power as the superlative British De Havilland Mosquito but the American bomber carried twice the Mosquito's maximum bomb load at the same speed as the British airplane. The Douglas bomber was also equipped with a powerful defensive armament that the Mosquito lacked.

Douglas designer, E.F. Burton, envisioned a bomber powered by two engines buried inside the fuselage. This design innovation could reduce the drag by one-third compared to more conventional bombers. When he compared his design to the Boeing B-29 Superfortress, Burton believed he could develop a faster airplane that would carry a similar bomb load and employ a crew of 3 instead of the 10 airmen needed to man the B-29. Burton believed his Mixmaster would require just half of the maintenance crew required to keep the Superfortress airborne and cost one-third the price of the large, four-engine bomber from Boeing."

.. not if you have an ejection seat! Also, you can install a pyrothecnic charge to blew off rudder and prop in case of ejection, like in the Do335.

Pusher prop 'canards' should have been the final evolution of 'Otto' aircrafts, and almost all Nations were working on such designs.
Dornier had drafted an evolution of the 335 with pusher contra-rotating props with incredible calculating figures (W Schick - I. Meyer Geheimprojekte der Luftwaffe: Jagdflugzeuge 1935-1945) along with several other designs from Messerchmitt-Lippisch (a variant if the Me163), Arado, Blohm Voss and others. Japan flew the Kyushu Shinden in 1945 and I bet that USA and UK had many other projects on going.
The point is that all this designs were still not in production when it was clear that the jet propulsion would had outperformed any prop evolution.

.. but as amateurs we had the Vary Eze from Burt Rutan that proved the potential of the formula!

I think it would have been pretty easy to fit one in the XB-42 though. As Joe kindly pointed out the U.S had an aircraft flying with an ejection seat in May 1944. They would have just stuck the same, or better, system in the XB-42.